1. Field of the Invention
This invention relates to a method and apparatus for soldering and, more particularly, to apparatus for automatically soldering electrical terminals.
2. Description of the Prior Art
A variety of automatic soldering apparatus for high production operation is presently known in the art. One system currently used employs a bath of molten solder through which the terminals to be soldered are passed. One particularly popular molten solder system is the wave soldering system in which a wave of molten solder is generated above the level of the molten solder bath with a circuit board carrying the terminals to be soldered being passed tangentially into contact with the surface of the wave. This system requires an appreciable amount of time to bring the solder bath to temperature and necessitates keeping the solder bath hot when there is no demand. This type of mass soldering also requires that steps be taken to minimize or preclude the formation of oxides on the surface of the molten solder bath. This method of soldering also is limited to use on circuit boards which are provided with connections to be soldered on one surface only, with no electrical components being on that side. Otherwise, electrical components on that side of the circuit board would be immersed in the molten solder which could render the components inoperative. Thus, mass soldering systems are limited to those applications in which high volume similar components can be designed with a surface adaptable for passing through or into contact with the molten solder bath.
In another system of automated soldering the components are precoated with solder and, when joined to form the connection, are heated by a flow of hot air or by the focussing of a laser or infrared beam on the joint to heat and melt the solder. This system suffers from the problem of surface oxidation before the joint is formed, resulting in joints which are unsatisfactory.
A third system of automatic soldering utilizes a soldering iron having a molten solder reservoir contained therein which is fed to the solder joint on demand. This system also suffers from the potential oxidation of the molten solder, resulting in less than adequate solder joints.
These last two systems of soldering suffer from the disadvantage that either flux is not employed to clean the surfaces to be joined, or additional, costly and complex apparatus is necessary to separately supply the flux at the appropriate time in the operational sequence.
Still another system of automatic high production solder apparatus utilizes a means for heating the soldering tip and/or the component to be soldered and advancing and feeding solder wire against the preheated part. It has been found that it is difficult to satisfactorily feed the solder wire to the component at the desired speed and yet obtain the necessary heating of both of the solder and the component. At the same time, oxidation of both the component and the solder has been a problem.
Furthermore, in the last noted system utilizing a solder wire feeding device, if flux-cored soldered wire were utilized, the melting temperature of the flux was sufficiently lower than the melting temperature of the solder that, by the time the solder had melted to form the joint, using e.g. 1/8 inch of solder, flux from 1/2 inch or more of the solder wire had been melted and had flowed out of the solder wire. Accordingly, and in addition to the mess created by the excess flux at that joint, subsequent solder joints would be formed without the benefit of flux to clean the joint surfaces before the solder was applied.